1. Field of the Invention
This invention relates to a photosensitive inkjet ink.
2. Description of the Related Art
In the preparation of the ink for an inkjet printer, pigment is employed as a colorant in order to improve the qualities of printing such as water resistance and light-resistance. Because of the feasibility of high-speed curing, because of limited volatilization of organic solvent and because of excellent adhesion, an ultraviolet curing type ink (UV ink) is now attracting many attentions.
As specific examples of the UV ink, the compositions comprising a radical polymeric monomer, a photopolymerization initiator and a pigment have been typically employed. There has been also proposed to employ a photopolymerizable UV ink comprising a cationic polymeric monomer, a photocation-generating agent and a pigment. Since these UV inks are enabled to form an ink layer which can be quickly non-fluidized as it is irradiated with light, it is possible to obtain a printed matter which is excellent in safety and in quality.
With respect to the recording by inkjet system, there is an increasing demand to perform the printing not only to a paper or resin substrate but also to a metal substrate. According to the conventional inkjet inks however, it has been impossible to form an ink layer which is sufficiently high not only in adhesion to a metal substrate but also in solvent resistance. In recent years, there has been tried to manufacture electronic parts such as a circuit board by printing, in which case, a circuit is formed on a resin substrate using a conductive material. If there is an ink which is capable of forming an ink layer having an excellent adhesion to metal substrate and exhibiting a sufficient strength, it would be possible to laminate both of an insulating material layer and a conductive material layer by printing. However, no one has succeeded to obtain such an ink as yet.
In recent years, inkjet ink is required to be excellent in safety in addition to excellent adhesion. The cationic polymerizable ink mentioned above generally comprises an epoxy compound as a polymeric monomer. Many kinds of epoxy resin indicate positive in the AMES test (a reverse mutation test where bacterias are employed). Because of this, epoxy resin is not necessarily safe in viewpoint of mutagenesis, etc. Although there are some kinds of epoxy resin which indicates negative in the AMES test, such epoxy compounds are limited in kinds. Moreover, the ink containing such epoxy compounds is not satisfactory in adhesion and in curing properties.
An ink incorporated with an epoxy compound indicating negative in the AMES test is also proposed. When a large quantity of alicyclic epoxy compound is included in the ink, there is a problem that it is impossible to obtain a sufficient solvent resistance.